Adenosine is known to be an endogenous modulator of a number of physiological functions. At the cardiovascular system level, adenosine is a strong vasodilator and a cardiac depressor. On the central nervous system, adenosine induces sedative, anxiolytic and antiepileptic effects. On the respiratory system, adenosine induces bronchoconstriction. At the kidney level, it exerts a biphasic action, inducing vasoconstriction at low concentrations and vasodilation at high doses. Adenosine acts as a lipolysis inhibitor on fat cells and as an anti-aggregant on platelets.
Adenosine action is mediated by the interaction with different membrane specific receptors that belong to the family of receptors coupled with G proteins. Biochemical and pharmacological studies, together with advances in molecular biology, have allowed the identification of at least four subtypes of adenosine receptors: A1, A2A, A2b and A3. A1 and A3 are high-affinity, inhibiting the activity of the enzyme adenylate cyclase, and A2A and A2b are low-affinity, stimulating the activity of the same enzyme.
Analogs of adenosine able to interact as antagonists with the A1, A2A, A2b and A3 receptors have also been identified. Selective antagonists for the A2A receptor are of pharmacological interest because of their reduced level of side effects. In the central nervous system, A2A antagonists can have antidepressant properties and stimulate cognitive functions. Moreover, data has shown that A2A receptors are present in high density in the basal ganglia, known to be important in the control of movement. Hence, A2A antagonists can improve motor impairment due to neurodegenerative diseases, for example, Parkinson's disease, senile dementia as in Alzheimer's disease, and psychoses of organic origin.
Some xanthine-related compounds have been found to be A1 receptor selective antagonists, and xanthine and non-xanthine compounds have been found to have high A2A affinity with varying degrees of A2A vs. A1 selectivity. Triazolo-pyrimidine adenosine A2A receptor antagonists with different substitution at the 7-position have been disclosed previously, for example in WO 95/01356; U.S. Pat. No. 5,565,460; WO 97/05138; and WO 98/52568.
Parkinson's disease is characterized by progressive degeneration of the nigrostriatal dopaminergic pathway. The subsequent reduction in striatal dopamine levels is responsible for motor symptoms associated with Parkinson's disease, e.g., the loss of fine motor control or motor impairment manifested in those suffering from the disease. Current methodologies for alleviating motor symptoms associated with Parkinson's disease seek to replace dopamine either within the presynaptic terminal, for example, by administration of L-Dopa, directly through stimulation of the postsynaptic D2 receptors, or by inhibiting metabolism, for example, by administration of monoamine oxidase type B (MAO-B) or catechol-O-methyltransferase (COMT). Long term use of such therapies is often associated with adverse events. For example, long term therapy with L-Dopa (currently the standard of care) is often associated with adverse events (e.g. motor complications), for example, “wearing-off”, “random on-off” oscillations, or dyskinesia. These motor complications arising from therapy administered to manage Parkinson's disease often become progressively more severe with continued treatment.
As mentioned above, A2A receptors are present in high density in the basal ganglia and are known to be important in the control of fine motor movement. Highly selective A2A antagonists have demonstrated their efficacy in reducing motor symptoms associated with neurodegenerative diseases. Accordingly, compounds that are A2A receptor antagonists are believed to be useful in alleviating motor symptoms associated with Parkinson's disease. For example, U.S. Pat. No. 6,630,475 to Neustadt et al. (the '475 patent) describes the preparation of the compound of Formula PI:

In the '475 patent, example Schemes 1 to 5, along with preparative Schemes 1 to 4, show general methods of preparing compounds of Formula PI. The '475 patent also describes that the compound of Formula I can be prepared as a pharmaceutically acceptable salt that may be useful for treating Parkinson's disease.
The use of A2A receptor antagonists in the treatment of central nervous system diseases, in particular Parkinson's disease, and pharmaceutical compositions comprising said compounds, has elevated the need for potent, moderately lipophilic, brain penetrant inhibitors of the A2A receptor. Such compounds would provide an expansion of the arsenal of compounds that are believed to have value in the treatment of central nervous system disorders, in particular treating or managing the progression of such diseases, for example, but not limited to, Parkinson's disease.